(a) Technical Field
Embodiments of the present invention generally relate to a thin film transistor and a manufacturing method of a display panel.
(b) Related Art
A liquid crystal display (LCD), a plasma display panel (PDP), and an organic light emitting device (OLED) are among widely used flat panel displays.
The LCD is a display device using electro-optical characteristics of liquid crystals in which light transmission amounts are varied according to the intensity of an applied electric field to thereby realize the display of images. The PDP is a display device for displaying images by using plasma generated by gas discharge. In the OLED, electrons and holes are injected into an organic illumination layer, respectively, from a cathode (the electron injection electrode) and an anode (the hole injection electrode). The injected electrons and holes are combined to generate excitons, which illuminate when converting from an excited state to a ground state.
In addition, as a display device that is widely used, a field emission display (FED) utilizing the tunneling effect of quantum mechanics to emit electrons from electron emission sources formed on cathode electrodes may be provided. The emitted electrons strike a phosphor layer formed on an anode electrode to illuminate the phosphor layer and thereby result in the display of images. An electrophoretic display (EPD) is a display device utilizing the electrophoretic phenomenon to repeatedly write or erase information made of symbols such as characters and numbers.
Among the flat panel displays, an active matrix type in which each pixel is independently controlled by including switching elements such as a thin film transistor is generally used. The thin film transistor may be classified as a top gate type and a bottom gate type according to the position of a gate electrode. Amorphous silicon and polysilicon are generally used as a material of a semiconductor forming a channel of the thin film transistor, wherein the amorphous silicon is widely used in the bottom gate type and the polysilicon is widely used in the top gate type.
In the bottom gate type, a gate electrode is disposed under a semiconductor member, and a source electrode and a drain electrode contact respective sides of the semiconductor member. The channel of the thin film transistor is formed in the portion that is disposed between the source electrode and the drain electrode in the semiconductor and is covered by an insulating layer.
When the channel of the thin film transistor, which is made of the semiconductor layer, is formed without a protection layer, the electrical characteristics of the thin film transistor are deteriorated by moisture or impurities incorporated from an atmosphere.
Particularly, in a COA (color filter on array) structure in which a color filter is formed on the same substrate as the thin film transistor, the organic layer of the color filter directly contacts the channel layer such that the channel layer is contaminated, and outgassing is generated from the organic layer of the color filter through a heat treatment of a following process such that a problem such as an image sticking is generated. Accordingly, an insulating layer is formed to prevent these problems, but the manufacturing process is complicated.